Model Test And Working Mechanism Study Of Suction Caisson In Clay

Suction caissons represent a new type of foundation, whi ch a re large cylindrical structures that open at the base and cl ose at the top. C ompared wi th traditional offs hore pile foundations, suction cai ssons ex hibit the adva ntages of shorter i nstallation periods, lower materi al costs, and m ore rational bea ring pattern s in cla y.Sucti on caissons have been successful ly employed in recen t years in many project s i ncludi ng mooring a nchor, brea kwa ter or sea walls, offshore platform a nd foundation for wind turbine. However, the complex interaction between a suct ion caisson a nd soil def ines the loading mecha nism of this foundation type, and its failure mode has yet to be clearly defined. Furthermore, there have been no standards for suct ion cais son designin g up to now. In this disserta ti on, the studies are emphasized on penetration characteristic and bea ring mechanism of s ucti on caisson in clay. The main i nvestiga tions consist of the foll owi ng parts:1. Model tests a re carried out to study the behavior of a sucti on cais son in di fferen t types of consol ida ted soils. Some key issues, such as jack and suction i nstallation, vertical beari ng capacity and uplift capacity, are investigated to elaborate t he working mechanism of suction cais son. The m odel test s provide a basis for the l ater research.2. Thi s paper presents the typical progresses over the world, and the principles a nd features of each simulating methods a re el aborat ed. The CEL fi nite element m ethod was perform ed t o simulate the ex periment proces s, and the res ults were consist ent with test da ta. The numerical simulating m ethods of penetra ti on in geotechnica l engi neerin g discus sed in this pa per a re a vailable to correla tive resea rchers.3. The penetration resi stance and soi l plug development are investiga ted with m odel test in laboratory. Based on model tes ts results, the caisson begi ns to install unt il t he applied suction greater than the require underpressure. When the applied suction i s grea ter t han the allowable underpressure, large soil may heave inside the cais son due to reverse end bea ring failure of soil plug.4. B ased on the FEM, the 3D numerical analys is is performed t o s imulate the working mechani sm and evalua te t he beari ng capacity behavior of suction caisson, ont he basis of which a calcul at ion method is presented for verti cal bea ring capacity of cais son. The conclus ions can provide references for the caisson bea ring ca pacity design.5. Due to the soil ins ide caisson, suction caisson and other ocean foundat ions show signif ica nt difference i n uplift characteris tics. There are three di fferen t failure m odes, “ slide failure”, “bottom resista nce failure ” and “reversed bea ring capacity fai lure”, for suction caissons subjected to pri ma rily vertical tensile loads. Different drai nage condi tions at the caisson base determ ine which failure mode is a pplicable.Efforts are made to i nvestiga te suction cais sons as a type of foundation for underwater structures. Ba s ed on the FEM, the numerical analysi s is performed to simulate the working mecha nism and eval uate t he resi stance percent under di fferen t pullout load.The optimum calculation method was als o provi ded through experiments and t heoreti c calculation.6. Finally, a numerical analysis is performed to sim ulat e the working mecha nism a nd evaluate t he bearing capacity behavior of suction caisson. Calcula tion result s show that the bearing characteristic s of suction caisson are different from those of the simpli fied lim it equilibri um method, and that failure occurs and devel ops in the soil wit hin the cai sson ski rt in the layered soil. This difference causes the s implified limit equili brium method to overestimate the bea ring ca pacity of suction cai sson.